Question 1206361
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The sequence is geometric.
a = -140 = first term
r = 0.5 = common ratio


{{{a[n] = a*(r)^(n-1)}}} = nth term of a geometric sequence, where n is a positive integer (1,2,3,4,...)


{{{a[n] = -140*(0.5)^(n-1)}}}


{{{a[20] = -140*(0.5)^(20-1)}}}


{{{a[20] = -0.00026703}}} approximately depending how you round it
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